1 hf radio links for hf radio links for rural telemedicine systems in developing countries arnau...
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HF radio links for HF radio links for Rural Telemedicine Systems in
Developing Countries
Arnau Sanchez SalaTechnical Researcher
February 2005
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WhatWhat is EHAS? is EHAS?The EHAS foundation is a non-profit institution, whose ultimate The EHAS foundation is a non-profit institution, whose ultimate goal isgoal is to contribute to the to contribute to the improvimprovement ofement of public health assistance public health assistance services in rural areas of Spanish American countriesservices in rural areas of Spanish American countries (but also (but also devolops useful technology for all developing country)devolops useful technology for all developing country)
EHAS FoundationEHAS Foundation
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How it does?How it does?
EHAS FoundationEHAS Foundation
IImproving work conditions for rural healthcare mproving work conditions for rural healthcare personnelpersonnel with a with appropriated telemedicine systemsppropriated telemedicine systems
TTelecommunications infrastructure in rural establishmentselecommunications infrastructure in rural establishments, , particularly those that particularly those that are the most isolated and lack phone line accessare the most isolated and lack phone line access..
Provision of information services for the healthcare system, aiming to offer: Provision of information services for the healthcare system, aiming to offer: Access to distance learning and qualification courses Access to distance learning and qualification courses Improving epidemiologic surveillance Improving epidemiologic surveillance Consultation to off-site personnel and medical experts Consultation to off-site personnel and medical experts Remote access to specialized medical informationRemote access to specialized medical information
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EHAS FoundationEHAS Foundation
Working linesWorking lines
Low cost communication hardware developing (voice Low cost communication hardware developing (voice and data).and data).
Introducing communication services and providingIntroducing communication services and providing access to medical informationaccess to medical information..
Introducing EHAS networks in real projects.Introducing EHAS networks in real projects. Evaluation of the Impact on Rural HealthcareEvaluation of the Impact on Rural Healthcare
WorkersWorkers..
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EHAS Data Radio NetworksHealth CenterHealth Post
Health Centre
Health Post
Health Post
Health Post
Phone Line
VHF Network (<40km)
HF Network
Isolated Health Post
Internet
EHAS Servers
VHF
VHF
VHF
HF
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HF CommunicationHF CommunicationIntroductionIntroduction
• Frequencies from 3 to 30 MHz
• Global communication coverage (cheaper than satellite communications)
• Unreliable and interrupted channels: - Time of day (day/night) -> D/F layer
- Season -> E layer
- Sunspot activity (11-year-cycle)
- Ionospheric storms
• Surface/Ionospheric propagation
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HF CommunicationHF CommunicationPropagation issuesPropagation issues
• Absorption (D-Layer for f < 7 MHz at day)
• Atmospherical noise
• Multipath -> Selective Fading
• Skip zones
• Critical frequencies:• MFU: Maximum Usable Frequency
(different for each layer)• LFU: Lowest Usable Frequency
(due to daytime D-Layer absorption)
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ICOM IC-78
HF CommunicationHF CommunicationComercial TransceiversComercial Transceivers
• Kenwood
• Yaesu
• ICOM
Kenwood TK-80
Main manufacturers
Yaesu FT-600
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HF CommunicationHF CommunicationCommercial modemsCommercial modems
• Amateur TNC (Terminal-to-Node Controller)
• SCS PTC-II
• Clover 2000
• CODAN 3012
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Commercial HF ModemsCommercial HF ModemsTNCTNC
• Modulation: 2-FSK
• Raw Data Rate: 300 bps
• Cost ~ 100 $
• Designed for VHF/UHF band
(Discarded)
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Commercial HF ModemsCommercial HF ModemsSCS PTC-IISCS PTC-II
• OFDM Modem
• Modulation: DQPSK
• Bandwidth: 2200 Hz
• Raw Data Rate: 200 to 3600 bps
• Error correction
• Cost ~ 1000 $
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Commercial HF ModemsCommercial HF ModemsClover 2000Clover 2000
• OFDM Modem
• Modulation: BPSK to 16-PSK
• Bandwidth: 2000 Hz
• Raw Data Rate: 375 to 3000 bps
• Error correction
• Cost ~ 1500 $
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Commercial HF ModemsCommercial HF ModemsCodan 3012Codan 3012
• OFDM Modem
• Modulation: QPSK
• Bandwidth: 2400 Hz
• Raw Data Rate: 2400 bps
• Error correction
• Cost ~ 6000 $
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Commercial HF ModemsCommercial HF ModemsConclusionConclusion
Disadvantages:• High cost• Propietary protocols
What we want:• Free GNU modem• Low Cost:
Software modem
Advantage:• Specially designed for
shortwave channels and HF transceivers.
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Soundmodem
Free HF ModemsFree HF Modems
Requeriments:• Free + Software Modem
Soundmodem:• GNU/GPL license• Uses standard soundcard
to modulate/demodulate• HF Modem: NewQPSK
FSK PSK
NewQPSK
P3D
PAM
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HF Modem: NewqpskHF Modem: Newqpsk• OFDM Modem
• 15 carriers / 2000 Hz
• Low multipath distorsion
• DQPSK modulation
• Error Correction: BCH (Block codes)
•Raw speed: 2500 bps (83.3 symbols/sec)
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HF Modem: NewqpskHF Modem: NewqpskBlock diagramBlock diagram
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HF Modem: NewqpskHF Modem: NewqpskPacket structurePacket structure
• Tune Phase: 380 msegs
• Sync Phase: 380 msegs
• Header: 12 msegs. (Packet length, FEC level)
• Data Phase: < 10 secs
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HF Modem: NewqpskHF Modem: NewqpskModificationsModifications
• Stronger Header Proteccion• Interleaved header
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HF Modem: NewqpskHF Modem: NewqpskModificationsModifications
• Enhanced Error Correction: Turbo Codes• Algorithm perfomance very close to Shannon Limit
• Encoding rate: from 1 to 1/3
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HF Modem: NewqpskHF Modem: NewqpskPerformancePerformance
• Bit Error-Rate for CCIR Channels (G/M/P)
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HF Modem: NewqpskHF Modem: NewqpskPPerformanceerformance
• SNR vs Packet Loss (1/3/5/10 iterations)
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Link Protocol: AX25Link Protocol: AX25
• Amateur X.25: Radio Link Layer Protocol
• Packet-switching with connected mode
• Error-free and packet order assured
• Free protocol (included in Linux Kernel)
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Link Protocol: AX25Link Protocol: AX25Modifications: ARQModifications: ARQ
ARQ: Automatic Repeat Request
• Go-Back-N: All info packets are asked to resent from a lost one. Very inefficient for high bit-error-rate channels.
Info 0
Info 1
Info 2
RR 3
Info 3
Info 4
Info 5
REJ 3
Sender Receiver
Info 3
Info 4
Info 5
Linux Implementation
2525
Info 0
Info 1
Info 2
RR 3
Sender Receiver
Info 3
Info 4
Info 5
SREJ 3
SREJ 4
Info 3
Info 4
Info 6
Link Protocol: AX25Link Protocol: AX25Modifications: ARQModifications: ARQ
• Selective REJect: Lost Packets are asked to reset with individual SREJ commands.
AX25 Version 2.2 Specification
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Info 1
Info 2
RR3
Sender Receiver
XSREJ 4,5, cont: 7
Info 4
Info 5
Info 7
Info 3
Info 4
Info 6
Info 5
Link Protocol: AX25Link Protocol: AX25Modifications: ARQModifications: ARQ
• eXtended Selective REJeject: Lost Packets are individually asked to be reset with a unique XSREJ command.
EHAS Implementation
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Link Protocol: AX25Link Protocol: AX25Modifications: DAMAModifications: DAMA
DAMA (Demand Assigned Multiple Access)
• Used for sharing the use of bandwidth among multiple users
• Uses TDM (Time Division Multiplexing)
• Server gives/removes turn to connected users
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Link Protocol: AX25Link Protocol: AX25 Modifications: DAMAModifications: DAMA
Health Centre
Health Post
Health PostHealth Post
SABM
UA
SABMUA RNR
SABM
UA
RNRINFO
AX25 packets
SABM: Asks for connection
UA: Accepts connection
RR: Peer can send data
RNR: Peer must wait
Health Post
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Health PostHealth Post
Link Protocol: AX25Link Protocol: AX25 Modifications: DAMAModifications: DAMA
Health Centre
Health Post
Health PostRNR
RR I
RNR
I
RR
INFO
RNR
Health Post
Health Post
AX25 packets
SABM: Asks for connection
UA: Accepts connection
RR: Peer can send data
RNR: Peer must wait
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HF ModemHF ModemLLink performance (NewQPSK + AX25)ink performance (NewQPSK + AX25)
• SNR vs Uncompressed speed
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Board interfaceBoard interface
• Interfaces between computer and radio– PTT (Push-to-talk)– Ignition– Channel selection
• Monitoring services:– Battery level– Battery charge– Radio temperature (controls a cooler)– Measures SWR (Standing-Wave-Ratio)
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HF ModemHF ModemHardware SchemeHardware Scheme
Computer
AX.25 SoundcardNewQPSK
Radio
USB
Interface Board
Antenna
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Services providedServices providedEmailEmail
• Electronic-mail is the most used data communication in EHAS networks
• Transmission requirements:• Resume broken transfers -> UUCP• Data compression -> BSMTP
• MTA (Message Transfer Agent)• Simple and secure -> POSTFIX
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Services providedServices providedEmailEmail
E-Mail Client Postfi
x
EHAS Modem
BSMTP
UUCP
Health Post
UUCPPostfix
BSMTP
Health Centre
InternetEHAS
Modem
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Services provided Services provided Proxy webProxy web
Web browsing
Chat
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Services providedServices providedProxy webProxy web
App using proxy web
EHAS Modem
TCP-AX25
Bridge
Health Post
Health Centre
EHAS Modem
TCP Tunne
l
TCP Tunne
l
TCP-AX25
BridgeInternet
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Linux installationLinux installation
Metadistro/Ubuntu
GNU/Debian based Hardware autodetection Live CD (with HD installation) Installation CD (only Ubuntu) Gnome Desktop Installed software: Gimp, OpenOffice,
Mozilla Browser/E-mail client
metadistros.hispalinux.e
s
www.ubuntulinux.org
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Pilot ProjectsPilot Projects
Currently pilot projects in Peru, Colombia and Cuba
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Pilot ProjectsPilot Projects
Dot matrix printerLaptop
Radio and modem Work table
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Other EHAS interestsOther EHAS interestsWiFiWiFi
• Speed: 1 to 11 Mbps.
• Originally designed for indoor use.
•Reach up to 20 Km.
• Voice, internet and video communication with Linux.
•EHAS is currently working on a solar router.
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EHAS Fundation: Rural Telemedicine in Latin America
countries
Thanks for your attentionThanks for your attentionE-mail contact: [email protected]